<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>盒子模型</title>
    <style>
        div{
            width: 200px;
            height: 300px;
            box-sizing: border-box;
            background-color: aquamarine;

            padding: 20px;
            border: 10px solid red;
            margin: 30px;
        }
    </style>
</head>
<body>
    <div>aaaaaaaaaaaaaaaaassssssssss</div>
</body>
</html>